1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device including silicon/germanium hereinafter abbreviated as SiGe) alloy.
2. Description of the Prior Art
Transistor devices are essential and ubiquitous in modern electronics. These devices possess the simultaneous qualities of bistability, high switching speed, low power dissipation, high-reliability, and scalability to very small dimensions. Current integrated circuits (ICs) provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of each individual device in the circuit and the spacing between device elements (the feature size) must be decreased.
The individual elements of the circuits, metal-oxide-semiconductor field effect transistor (hereinafter abbreviated as MOSFET) devices and other passive and active circuit elements, must be interconnected by metal or other conductors to implement the desired circuit function. Some small resistance is associated with each contact between the conductor and the circuit element. As the feature size decreases, the contact resistance increases and becomes a greater and greater percentage of the total circuit resistance. As feature sizes decrease from 150 nanometers (nm) to 90 nm, then to 45 nm and below, the contact resistance becomes more and more important. At feature sizes of 32 nm, the contact resistance likely will dominate chip performance unless some innovation changes the present trend. It is therefore an imperative issue to reduce the contact resistance.